The present invention relates to a shoe for a hoofed animal, such as a horseshoe, and to a method for shoeing a hoofed animal, such as a horse.
The hoof on the foot of a horse comprises a curved covering of horn which protects the front of, and partially encloses, the end of the corresponding digit of the horse. It thus corresponds to a nail on a finger or toe of a human being. The forward end of the hoof is known as the toe, from which the side walls of the hoof extend rearwardly to a heel on either side of the horse""s foot. The hoof surrounds a body of tissue which surrounds the digit itself so as to form a capsule, the underside of which forms the sole. Between the hoof and this body of tissue there is an intermediate layer of tissue called the white line. At the rearward end of the horse""s foot there is an elastic horny pad of generally triangular shape which is known as the frog.
Domesticated horses are normally shod with horseshoes. A horseshoe is usually attached by nailing to the underside of the hoof to protect it from damage. Conventional horseshoes for horses with healthy feet are made from metal, such as cast iron, steel, or an aluminium alloy. One common design of horseshoe is generally arcuate in shape and sized so as to conform to the size of the hoof to be shod. The size and weight of the horseshoe is normally determined by the type of horse being shod. For example, a working horse will be fitted with heavier shoes than a racehorse. In some designs there may be an upstanding tab at the front of the shoe, or a pair of upstanding tabs positioned one to each side of the front of the shoe, designed to assist in locating the shoe on the hoof and to provide additional protection for the toe of the horse""s foot. Other designs of metal horseshoe are known, for example, so-called egg, straight and heart-bar shoes; these are often recommended for use on horses with hoof or lameness problems.
The traditional way of making horseshoes is for the farrier to forge them from bars of iron which are heated on an open hearth forge, hammered to shape on an anvil, and pierced to provide holes for the horseshoe nails. A farrier can produce shoes in advance for fitting to a horse with healthy feet which he has shod previously and whose hoof measurements he already knows. Alternatively he can purchase factory made shoes which can in suitable cases be fitted as received to a horse with healthy feet or which may require to be modified somewhat in shape, or in the position or direction of the holes for the horseshoe nails, using a forge and anvil. Often the horse will be brought to the farrier""s smithy to be shoed but many horses are shod at their owner""s premises, in which case the farrier will normally bring a portable forge with him in case of need.
Plastics and rubber horseshoes are also known in the art, particularly for shoeing horses suffering from hoof problems. For example, rubber shoes made from a shock-absorbing rubber bonded to a steel or aluminium core are available on the market, as are also horseshoes made from polyurethane and from plastics moulded on to an aluminium core. Some of these mimic the form of the conventional metal shoes and, likewise, are attached to the hoof by nails. Another type of currently available horseshoe is sold in kit form, using polyurethane base plates that have to be cut to the shape of the horse""s hoof. Plastics tags are then welded at intervals to the outer rim of the base in an upwardly and radially inward fashion. The shoes are then attached to the hoof by cementing the plastic tags to the outer wall of the hoof. Plastics horseshoes have a number of advantages over metal shoes; for example, they are lighter and can be affixed to a horse""s hoof by glueing instead of nailing. Thus they are beneficial for use when a horse is suffering foot problems because they obviate the use of nails. Such foot problems may include laminitis, white line disease (or fungal onychomycosis), navicular disease, sand cracks, or weak heels. Laminitis is a painful condition in which the hoof becomes partly detached from the rest of the hoof capsule along the white line. This can be accompanied by splitting of the hoof. Driving a nail into a hoof in such a condition can exacerbate the problem besides being painful for the horse.
In order to treat an injury to or a disease of a horse""s foot, it is usual to cut or abrade away the affected material. Since the pathogens which attack the hoof are generally anaerobic, this helps to speed up a cure. However, there is then the problem of providing support to the trimmed hoof so that the horse can still put weight on its foot without undue discomfort and without exacerbating any misalignment of the horse""s leg or, in particular, of the digital bone of the foot, due to the lameness condition from which the horse is suffering. This support can be provided by use of a therapeutic shoe and by using a hoof replacement material to replace the parts that have been cut or abraded away. If the farrier elects to fit a metal shoe then he may have to undertake considerable work to forge a horseshoe of the appropriate shape. If he decides to opt for a plastics or rubber shoe then he may have to cut the shoe to shape or use chemicals with undesirable side effects in order to provide a replacement for the hoof material and any tissue that has been cut or abraded away. If the farrier decides that the horse""s foot needs realignment he may decide to provide the horseshoe with a lateral, medial, anterior or posterior extension. This is difficult to effect with a preformed horseshoe.
Foals are sometimes born with deformities such as weak flexor tendons, or club foot syndrome, or may require treatment to correct toe in or toe out conformation. In such instances the farrier will often fit the foal with corrective shoes. One type of foal corrective shoe is formed entirely from a heavy duty plastics material with an upstanding outer cuff which is glued or cemented to the hoof wall. Such shoes can be provided with an appropriate wedge shape and/or with an appropriate lateral, medial, anterior or posterior extension to correct the condition being treated. It has also been proposed to use therapeutic cuffs which can be glued or cemented to the outer wall of the hoof after an appropriate metal shoe has been rivetted to it or to which a shoe can be carefully nailed.
In some cases the farrier may choose to put a pad of leather or of an elastomeric material between the hoof and the horseshoe.
European Patent Specification No. 0 893 057 A1 discloses an open plastic horseshoe with holes for nails and having a bridge piece positioned on one arm for adjustment of the distance between the two arms of the horseshoe.
Use for shoeing a horse of a preformed strip of L-section adhered to a lower wall of its hoof and then adhering a plastics horseshoe thereto is proposed in New Zealand Patent Specification No. 184321.
A horseshoe adhered to a hoof is described in New Zealand Patent Specification No. 221274.
In German Patent Specification No. 19732269 there is taught a horseshoe with an outer hoof cover used as the walking surface which is secured to the hoof by at least two elements. A contact strip binding forms an intermediate layer between the hoof surface and the outer hoof protection. The hoof protection can be made from a thermoplastic material, such as polyester, or vinyl ester, or from an elastomer or a metal.
International Patent Publication No. WO99/15006 describes a helical stock from which circumferential lengths can be cut to be used as horseshoes, the stock comprising a helical coil of plastics material wound about an axis such that the cross section of the coil in a plane containing the axis is constant in shape for any such plane and substantially corresponds to the cross section of a horseshoe in the same plane.
British Patent Specification No. 2334424 teaches a horseshoe having a metal core with a polyurethane coating.
U.S. Pat. No. 5,199,498 proposes a custom horseshoe pad comprising a polymer composition containing at least about 50% by weight of high molecular caprolactone polymers wherein the composition has a melting point of from about 120xc2x0 F. to about 200xc2x0 F. (about 48.9xc2x0 C. to about 93.3xc2x0 C.). The molecular weight of the caprolactone polymers can range, for example, from about 35,000 to about 60,000. The pad covers areas of the horse""s foot that are sensitive and vulnerable to disease and damage. The horseshoe pad is positioned between a horseshoe and the hoof and is intended to expand the overall protection afforded by the standard horseshoe without obviating the need for the shoe.
In U.S. Pat. No. 5,681,350 there is described a rigid and permeable prosthesis that fills the debrided portion of the wall of a horse""s hoof having white line disease or the like. This prosthesis includes a mass of particulate material with individual particles coated with a resin so as to cleave to one another at all contact areas and transfer weight, while leaving interconnected pore spaces that allow air and liquid medications to reach the diseased area during the healing process.
International Patent Publication No. WO 94/06285 proposes a lightweight plastic horseshoe which is held to the bottom of a horse""s hoof by gluing it thereto and by additionally providing preformed spaced depressions in the underside of the hoof into which extend fasteners attached to the shoe.
In International Patent Publication No. WO 94/12024 a protective covering for a horse""s hoof is described which comprises a horseshoe made of polyurethane having convex and concave edges and a polymeric fabric, for example a woven polyurethane fabric, bonded to the horseshoe. The shoe is fitted to the horse""s hoof and secured thereto using an acrylic structural adhesive both between the hoof and the shoe and between the polymeric fabric and the outside of the horse""s hoof.
A horseshoe with a core of metal which is surrounded by a plastic or rubber material and has apertures for intended for nails is suggested in International Patent Publication No. WO 94/22296.
In International Patent Publication No. WO 95/22252 there is proposed a method of shoeing a horse in which a particulate compound comprising a ground up polymer and an adhesive compound. This particulate compound is poured into a mould into which the horse""s hoof, which has previously been cleaned and had an adhesive applied to all voids, is lowered.
International Patent Publication No. WO 96/01044 is concerned with a horseshoe having holes for horseshoe nails and including a resilient material.
Another proposal is to be found in International Patent Publication No. WO 98/24312. This comprises a core of metal with holes for horseshoe nails which is substantially entirely enclosed in a substantially deformable material such as a rubber or rubber-like material.
A hoof protector for hooves of horses is suggested in International Patent Publication No. WO 99/40782 which has a horseshoe shaped base body of plastic and at least one fixed front setting element.
International Patent Publication No. WO 99/65298 describes a shock-absorbing horseshoe which is secured to a horse""s hoof with nails whose nailheads abut against an intermediate resilient layer.
European Patent Specification No. 0 651 943 A1 teaches a boot for horses"" hooves made of flexible material.
A plastic covering for a horse""s hoof with a two part laminate construction for attachment to the hoof of a horse using nails is disclosed in European Patent Specification No. 0 823 209 A2. The upper layer comprises a stable plastic material, such as a thermally formable plastic (e.g. polyurethane, polyamide or an elastomer), while the lower layer is less hard and is also formed from a plastic.
European Patent Specification No. 0 832 560 A1 teaches a horseshoe which is at least partially enclosed in a resilient material which has holes for conventional nails.
European Patent Specification No. 0 860 115 A1 discloses a horseshoe with a shock-absorbing sole plate with a peripheral indentation for receipt of a steel band to which are fixed six supports through which nails can be driven into the horse""s hoof.
As pointed out above most, if not all, plastics horseshoes currently on the market suffer from the disadvantage that they are time-consuming and cumbersome to apply, particularly those that have to be assembled from a kit of parts. This is at least in part due to the necessity to make the horseshoe fit a damaged foot from which a considerable amount of hoof may have been cut away. Since the horse is lame it will usually be inconvenient or impractical for it to be brought to the smithy so that the farrier has to take his equipment to the horse""s own stable. This tends to make it more inconvenient for the farrier to have to reshape a horseshoe away from his own smithy.
There is accordingly a need in the art for an improved form of horseshoe which can be used in therapy for treatment of such diseases as laminitis and which is simple to apply to the foot of a horse being treated. There is a further need for a novel design of horseshoe which can be readily adapted to fit and provide support for a foot of a hoofed animal from which a variable amount of hoof material, and possibly also other tissue, may have been cut or abraded away. There is still further a need for a horseshoe which can be readily formed to an appropriate shape for treatment of a horse that is suffering from foot problems, particularly when such shaping has to be accomplished in the horse""s own stable or stableyard rather than at a farrier""s smithy. Additionally there is a need for a horseshoe which can be fitted to the hoof of a horse suffering from laminitis or other condition causing lameness without the use of nails and in a manner which substantially avoids trauma for the horse. Yet again there is a need for an improved method of shoeing a horse that obviates the need to drive nails into the hoof of the horse. There is also a need for a method of shoeing a horse suffering from a debilitating condition, such as laminitis, which avoids trauma for the horse. Moreover there is a need to provide a novel method of shoeing a horse which avoids the use of a forge. Another need is for a method of shoeing a horse which utilises horseshoes which can be moulded to a hoof and attached thereto in a simple manner without use of a forge.
The present invention accordingly seeks to provide an improved form of horseshoe which is suitable for use in treatment of laminitis and other conditions for which horse""s feet may require treatment and which is simple to apply to the foot of a horse being treated. It further seeks to provide a new form of horseshoe which can be readily shaped or otherwise adapted to fit and provide support for a foot of a hoofed animal from which hoof material, and possibly also other tissue, has been cut or abraded away. In addition it seeks to provide a horseshoe which can be readily formed to an appropriate shape for treatment of a horse that is suffering from laminitis or other foot problems. It seeks moreover to provide a horseshoe which can be formed quickly and simply to an appropriate shape even under the unfavourable conditions which may exist in a horse""s own stable or stableyard, rather than in the convenient surroundings of the farrier""s own smithy. It also seeks to provide a plastics horseshoe that is more easily fitted to the hoof, with an improved fitting quality and the additional support required for therapeutic purposes. Additionally it seeks to provide a horseshoe which can be fitted to a horse""s hoof without nailing and in a manner which minimises any trauma for the animal. An additional objective of the invention is to provide a novel and improved method of shoeing a hoofed animal, such as a horse, without use of nails driven through the shoes into the animal""s hoof. A still further objective is to provide a novel and improved method of shoeing a horse without causing trauma to a horse which may be suffering from a debilitating and painful condition, such as laminitis. Yet another objective is to provide such a method which avoids use of a forge. There is also the objective of providing a novel and improved method of shoeing a horse which utilises horseshoes which can be moulded to the hoof of a horse and attached thereto without requiring use of a temperature high enough to require use of a forge.
According to one aspect of the present invention there is provided a shoe for a hoofed animal comprising a body made from a thermoplastic composition which comprises a matrix of a thermoplastic material which has a softening point of less than 100xc2x0 C.
The invention further provides a method of shoeing a hoofed animal which comprises:
(a) providing a shoe for a hoof of the animal, the shoe comprising a body which is made from a thermoplastic composition which comprises a matrix of a thermoplastic material having a softening point of less than 100xc2x0 C. and which has a lower ground-contacting surface for contact, in use, with the ground and an upper foot-contacting surface spaced from the lower ground-contacting surface for contacting, in use, the underside of a foot of a hoofed animal, the body having around at least a part of its upper foot-contacting surface an upstanding peripheral flange portion, and the shoe being adapted to be fitted, in use, on an underside of the hoof with the flange portion extending upwards from a ground border of the hoof adjacent a lower portion of an outer horny wall of the hoof;
(b) forming a plurality of indentations in the lower portion of the outer horny wall of the hoof;
(c) heating the shoe to a temperature sufficient to soften the thermoplastic material but below its melting point;
(d) placing the heated shoe against the underside of the hoof with its flange portion adjacent the lower portion of the outer horny wall of the hoof; and
(e) pressing the flange portion of the heated shoe into contact with the outer horny wall of the hoof so as to cause material of the flange portion to enter each of the plurality of indentations, whereby following cooling of the shoe the shoe is retained on the hoof.
The thermoplastic material is desirably chosen so that the thermoplastic composition is hard at ambient temperatures and at hoof sole temperatures but is softenable by immersion in hot water, preferably boiling water or near boiling water. In addition it should desirably possess at least moderate abrasion resistance. The thermoplastics material preferably has a melting point or a melting point range of less than 100xc2x0 C. Even more preferably it has a freezing point of at least about 30xc2x0 C., preferably at least about 35xc2x0 C., and a melting point or melting point range of less than about 95xc2x0 C., more preferably less than about 90xc2x0 C., and even more preferably less than about 75xc2x0 C. One particularly preferred material is a polycaprolactone. Polycaprolactones are commercially available under the trade marks CAPA(copyright) from Solvay Interox Limited, Baronet Road, Warrington, Cheshire WA4 6HB, United Kingdom and TONE(copyright) from Union Carbide Corporation of 39 Old Ridgebury Road, Danbury, Conn. 06817-0001, United States of America. The materials sold under the trade mark CAPA(copyright) are sold in granule form and are described as polyesters of xcex5-caprolactone and butane-1,4-diol. A particular advantage of the use of a polycaprolactone is that it is fully biodegradable. One suitable material is a polycaprolactone having a freezing point of about 35xc2x0 C., and a melting point range of from about 58xc2x0 C. to about 60xc2x0 C. Such a material has a molecular weight of from about 48,000 Daltons to about 52,000 Daltons and is sold under the trade designation CAPA(copyright) 650 polycaprolactone. It is also possible to blend CAPA(copyright) 650 polycaprolactone with minor amounts, for example up to about 25% by weight or more, e.g. up to about 40% by weight, of another polycaprolactone such as CAPA(copyright) 680 polycaprolactone and/or with lesser amounts, for example up to about 10% by weight, of CAPA(copyright) 640 polycaprolactone. CAPA(copyright) 680 polycaprolactone is reported to have a melting point of about 60 to 62xc2x0 C. and a molecular weight of about 80,000 Daltons, while CAPA(copyright) 640 polycaprolactone is reported to have a melting point of from 58 to 60xc2x0 C. and a molecular weight of about 37,000 Daltons. A particularly preferred thermoplastic material comprises a mixture of about 2 parts by weight of CAPA(copyright) 650 polycaprolactone and about 1 part by weight of CAPA(copyright) 680 polycaprolactone.
A preferred form of shoe according to the invention comprises a body moulded from a thermoplastic composition which comprises a matrix of a thermoplastic material having a freezing point of at least about 30xc2x0 C. and a melting point or melting point range of less than about 95xc2x0 C., the body having a lower ground-contacting surface for contact, in use, with the ground and an upper foot-contacting surface spaced from the lower ground-contacting surface for contacting, in use, the underside of a foot of a hoofed animal, such as a horse, the body having around at least a part of its upper foot-contacting surface an upstanding peripheral flange portion adapted in use to abut against at least a part of the outer wall of the foot of a horse or other hoofed animal. In such a shoe intended for use on a horse, the body may comprise an arcuate bar portion shaped to underlie the hoof. In addition the two ends of the bar portion may be joined one to another by a crosspiece. Moreover the shoe may include a frogpiece intended to underlie the frog of the horse""s foot and which may be provided with a cut out portion that extends from the rearward end of the frogpiece part way towards the front end of the frogpiece so as to facilitate flexing of the shoe. If desired, the flange portion may include an upstanding rear flange portion adapted to abut against the heels of the hoof. Such a shoe can be moulded as a one piece moulding. It can have a chamfered portion on its underside at its front end which underlies the toe of the horse""s hoof, in use. Otherwise the under surface of the shoe may be substantially planar.
The flange portion may be continuous or discontinuous. It may be adapted so as to extend, in use, from one side wall around the toe of the horse""s hoof to the other side wall. Alternatively the flange portion may be adapted to extend, in use, from the toe of the horse""s hoof back towards each of the heels thereof a distance which is less than the overall peripheral distance from the toe to the heel. Instead of a continuous flange portion it is possible to utilise a plurality of tab portions or to use a flange portion whose height varies along its length, such as a crenellated flange portion.
The flange portion may taper in section from its root towards its upper free rim portion. Thus, for example, it may taper in section from a thickness of about 5 mm at its root to about 3 mm at its upper free rim. Typically the body is about 10 mm deep and the flange portion extends upwards for about 20 mm, making the overall height of the horseshoe about 30 mm. It can be made in a variety of sizes. For example, it may measure about 125 mm from front to back and about 105 mm across. However, larger sizes, e.g. for carthorses, or smaller sizes, e.g. for use in correction of foal""s foot deformities, can be produced in accordance with the teachings of the invention.
In use of a horseshoe of the invention, the farrier typically first removes any hoof and tissue that may be damaged. Then the horse""s hoof can be treated by rasping a number of horizontal key-in lines around the bottom 2 to 3 cm or so of the outer wall. The wall of the hoof is then cleaned with acetone or, preferably, surgical spirit, prior to which the farrier should don protective gloves. Latex gloves are suitable. A horseshoe of the appropriate size according to the invention is then selected and the toe can, if necessary, be worked to create a bevelled edge at the front of the shoe, sloping in an upwardly outward direction from the underside, to provide a larger ground bearing surface area and to facilitate clearance of the toe of the hoof over the ground, thereby reducing the risk of the horse jarring its infected foot. This process can alternatively be performed after the horseshoe has been fitted.
The horseshoe is then placed into a non-reactive liquid, e.g. water, which has been raised to a temperature greater than the freezing point of the thermoplastic material and preferably above its softening point or softening point range. Hence the temperature of the water or other liquid is preferably at least about 60xc2x0 C. and preferably at least about 80xc2x0 C. In practice it has been found that a bucket filled with boiling or near boiling water will retain sufficient heat to enable fitting of at least one horseshoe to be completed. The thermoplastic material remains in the liquid until it becomes soft and pliable. This is characterised by the flange of the horseshoe turning transparent. The horseshoe is removed from the liquid before the entire mass turns transparent so as to ensure that it retains its form. This usually takes less than 2 minutes, e.g. about 90 seconds, depending upon the size of the shoe, the temperature of the water and the material used.
Alternatively some other means of heating the thermoplastic material can be used, such as a blow torch or hot air blower. However, the use of hot water has the advantage that it reduces the tackiness of the softened horseshoe and hence of it sticking to the farrier""s gloves or other objects with which it may come in contact.
When the horseshoe has softened sufficiently to become manually deformable, the horseshoe is then fitted to the horse""s foot by pressing the softened shoe firmly onto the hoof thereby deforming the upper surface of the horseshoe to fit the horse""s foot and by pressing the flange portion against the outer surface of the hoof horn outer wall. It is preferable to apply the softened horseshoe heel end first, using the frog as a datum. Special care should be taken to ensure that the shoe is moulded tightly round the hoof. The flange is arranged such that it is in continuous contact with the wall of the hoof around at least a part of its circumference. The flange may extend towards each heel of the hoof only a part of the overall distance from the toe to the heel of the hoof. In this case the heel is free to flex somewhat in use as the horse moves. Alternatively the flange portion can extend substantially the entire distance from the toe of the hoof to its heel on each side of the hoof. In this case the flange portion can be bonded to the hoof, or what remains of it, around the entire periphery of the hoof from one heel to the other. Moreover it can in this latter case also continue across the rear of the horseshoe so that it extends across the rear of the horse""s foot.
Each horseshoe can thus be moulded so as to be custom made to match the unique features of each hoof. In addition, if the farrier wishes to build up the horseshoe at any point it is a simple matter to soften some additional polycaprolactone material and then, after cleaning the hoof if necessary, to press the additional material on the softened shoe in the appropriate place.
When the shoe has been satisfactorily shaped to the horse""s hoof a rapid coolant can be applied which causes the thermoplastic to re-solidify. Suitable coolants are sold in aerosol dispensers for use in plumbing. A suitable coolant is available from Poynton Ltd, of 60 High Street, Malmesbury, Wiltshire SN16 9AT under the trade mark IMPRINT(trademark). This product is described by its suppliers as a self-propelling mixture of not more than 10% dimethyl ether and the balance 1,1,1,2-tetrafluoroethylene. Re-solidification of the horseshoe is characterised by the horseshoe becoming opaque again as it hardens.
The shoe can be cemented to the hoof by application of a suitable bonding agent between the flange of the horseshoe and the hoof. Suitable bonding agents include those sold under the trade marks Equithane(trademark) and Bond-N-Flex(trademark). A particularly preferred bonding agent is that available under the trade mark IMPRINT(trademark) from Poynton Ltd, of 60 High Street, Malmesbury, Wiltshire SN16 9AT, which is described as a two-part methacrylate adhesive whose components comprise not more than 55% by weight methyl methacrylate and not more than 8% by weight methacrylic acid. The bonding agent can be applied between the flange portion over its entire length. Hence, in one form of horseshoe, bonding agent can be applied over the entire periphery of the hoof, from heel to heel, such that the bonding agent is lipping the top of the flange. In other designs, however, the flange portion does not extend back as far as the heels so that it is adhered to the hoof, or what remains of it, only over a part of the entire periphery of the hoof. Application of the bonding agent can be achieved by prising the edge of the flange away from the hoof wall and injecting the bonding agent into the cavity.
Alternatively and more usually a bonding agent can be applied to the flange portion of the softened horseshoe and normally also to the hoof horn outer wall against which the flange portion is to abut before the horseshoe is applied to the horse""s hoof.
It is an advantage of the IMPRINT(trademark) bonding agent that it can be applied to the softened horseshoe immediately after it has been taken out of hot water, even though it is still wet.
It will usually be advantageous to warm the bonding agent somewhat prior to application so as to speed up curing thereof. The horizontal key-in lines rasped into the wall of the hoof improve the grip of the bonding agent on the wall. Attaching the horseshoe to the hoof in this way prevents the damage caused by nailing the shoe in place.
Any final adjustments can then be made to ensure a comfortable fit for the horse.
It is to be understood that the present invention is not restricted to shoes for horses but includes shoes for any hoofed animal. Hence the teachings of the invention can be applied with equal success to shoes for such hoofed animals as donkeys, mules, zebras, and cows.
The thermoplastic composition may further comprise a minor amount (e.g. from about 1% by volume up to about 25% by volume) of a filler material, such as a dye or a rubber in crumb, chunk, or granule form.
If desired, the underside of the shoe can be provided with one or more rubber inserts therein.